Various hand-held devices are known which utilize a granular purifying agent which is insoluble in water, such as activated charcoal and/or an ion exchange material for the purification of water. Examples of such devices are: U.S. Pat. No. 4,306,971 (Hankammer); U.S. Pat. No. 4,895,648 (Hankammer); U.S. Pat. No. 4,969,996 (Hankammer); U.S. Pat. No. 5,049,272 (Nieweg): and, PCT published Application No. WO 96/31440 (Serenko et al.).
Generally, these devices comprise a large funnel-shaped member to hold and channel the water to be purified, a removable filtration cartridge placed in the flow channel of the funnel-shaped member, and a collection beaker for the purified water. The filtration cartridges are typically constructed from inexpensive plastics materials and comprise a substantially frustoconical hollow vessel member capped by a hollow cover member, which vessel member and cover member together define a container for receiving and retaining the granular purifying agent therein. The cover member includes an annular inlet portion extending upwardly and inwardly from a peripheral rim portion, and topped by a substantially flat-topped central portion. The annular inlet portion has a multiplicity of vertically oriented water entry flow slots arrayed therearound to permit water to enter into the hollow vessel member whereat the water comes in contact with the granular purifying agent which is typically an ion exchange material. A screen-like end wall portion is typically disposed at the lower end of the hollow frustoconical vessel member below the granular purifying agent to permit the filtered water to pour into the collection beaker.
All known granular purifying agents have a maximum cumulative filtering capacity, or in other words lose their effectiveness after filtering a predictable amount of water, typically after about a month of normal household usage (i.e., after about 100 litres of water have been filtered). Accordingly, such filtration cartridges are designed to be discarded after a rather short period of time. In order to maximize the volume of water that a predetermined amount of granular purifying agent can effectively treat, thereby lengthening the time that a filtration cartridge can be used, it is necessary to effectively and fully use the entire mass of the granular purifying agent during filtration.
Further, the rate of flow of water through the filter cartridge is critical for effective water purification. It is necessary to contain the water within the filtration cartridge for a sufficient time to allow for effective ion exchange and filtration to occur, yet if the flow rate of water through the cartridge is too slow, then an insufficient volume of water will be purified, in a time frame which is satisfactory to the user of the filtration system. In order to minimize the length of time of filtration, yet still achieve full and proper filtration, it is necessary maximize the amount of filtering per unit time. To accomplish this, it is necessary to use the entire volume of the active granular purifying agent within the filter.
It has been found, however, with all types of prior art hand-held water filtration devices, that water tends to adhere to the inner surface of the hollow cover member after it flows through the water entry flow slots therein, in the sense that it tends to flow down the inside surface of the hollow cover member as the water makes its way toward the granular purifying agent. As such, much of the water therefore contacts the granular purifying agent in the peripherally disposed region adjacent the interior wall surface of the vessel member holding the granular purifying agent. Accordingly, a significant radially inner portion of the granular purifying agent receives substantially less water volume than the peripherally disposed region adjacent the inner wall surface of the hollow vessel member, thus very significantly underutilizing the capacity of the whole mass of granular purifying agent. As a result of this phenomenon, it has been found that, with conventional hand-held water filtration devices of the type described above, that a significant portion of the granular purifying agent towards the centre of the water filter cartridge remains chemically active within acceptable ranges, while the chemical activity of the outer peripheral ring of granular purifying agent adjacent to the inner wall of the hollow vessel member has deteriorated to the point that the water filter cartridge must be discarded. Moreover, it has also been found that settling of the granular purifying agent occurs unevenly toward the centre of the filter cartridge, so as to cause more dense packing of the granular purifying agent toward the centre of the cartridge. This causes a zone of least resistance to water flow adjacent to the inner wall of the hollow vessel member, with the result that the water being filtered tends to remain near the peripherally disposed interior surface of the hollow vessel member as it passes through the granular purifying agent from top to bottom. Moreover, uneven wetting of the granular purifying agent levels to cause the formation of air pockets within the granular purifying agent, which can of course, impede water flow rates through the filter cartridge.
It is therefore an object of the present invention to provide an improved water filter cartridge which overcomes these and other problems associated with prior art water filter cartridges.
It is another object of the present invention to provide an improved water filter cartridge that maximizes the volume of water that a predetermined amount of granular purifying agent can effectively filter before being discarded.
It is a further object of the present invention to provide an improved water filter cartridge that can be used for a longer period of time than prior art filter cartridges before expiry of the same mass of granular purifying agent.
It is yet another object of the present invention to provide an improved water filter cartridge that uses substantially the entire mass of the granular purifying agent during filtration.
It is yet a further object of the present invention to provide an improved water filter cartridge wherein the flow rate of water through the filtration cartridge permits a sufficient volume of water to be purified in a time frame which is satisfactory to the user, yet still achieves full and proper filtration and resists the formation of trapped air within the granular purifying agent.
It is yet another object of the present invention to provide an improved water filter cartridge that maximizes the amount of filtering of water per unit time.